What is the ruling on taking a commission percentage from a partner in exchange for referring a client to him to execute a design, without the client's knowledge?

There is no objection to taking a commission from the executor for referring the project to him, and there is no condition to inform the client of this; because the agreement with the client was clearly made on the wages for planning and execution, and the commission is deducted from the executor's profit without the client having any involvement in it.